The United States annually consumes about 90 ExaJoules (EJ) of carbon-based fuels, 88% of its total energy consumption in 2008. The use of these fuels is supported by heavily capitalized processing, distribution and utilization industries.
The sustainability of these systems is questionable on two counts. First, the US imports 25% of the energy it uses, a proportion that is projected to increase substantially. Imported energy is obtained from sources that are under pressure to serve increasing demand from growing economies in other parts of the world. Second, more than 96% of the carbon-based fuels are obtained from fossil reserves, which are finite. Useful energy is obtained from carbon-based fuels by oxidizing reduced states of carbon to carbon dioxide. For fossil fuels, this process is basically open-loop, producing CO2 with no compensating carbon reduction process to close the cycle. The consequent gradual accumulation of atmospheric CO2 is beginning to cause changes in the global climate that threaten many aspects of our way of life. Therefore, a process that can close this carbon energy cycle for the total energy economy is needed.
An annual flux of 58,000 EJ of solar energy strikes US soil, making it our most abundant carbon-free energy resource—500 times current consumption. Solar energy has the unique advantage of being a domestic resource not just in the US, but everywhere that people live. Its widespread use as a primary resource would secure energy independence throughout the world. Nevertheless, today solar energy is only a marginal component of the energy economy, providing less than 0.1% of marketed US energy consumption. Exploitation of solar energy is limited principally because it is intermittent and cannot be relied upon to provide the base-load energy that must be available whenever needed. What is lacking is a method for storing solar energy in a stable form that can be tapped whenever needed. Ideally, such a storage form should fit smoothly into the existing energy infrastructure so that it can be quickly deployed once developed.
There is a need in the energy industry for systems to convert one form of energy into another. In particular, there is a need for systems to convert electricity into a form of energy that can be stored inexpensively on industrial scales. Many sources of electricity generation cannot be adjusted to match changing demand. For example, coal power plants run most efficiently when maintained at a constant rate and cannot be adjusted as easily as natural gas (methane) fired power plants. Likewise, wind turbines generate electricity when the wind is blowing which may not necessarily happen when electricity demand is highest.
There is also a need to convert electricity into a form that can be transported long distances without significant losses. Many opportunities for wind farms, geothermal, hydroelectric or solar based power generation facilities are not located close to major population centers, but electric power losses over hundreds of miles add significant cost to such distant power facilities.
Methane is one of the most versatile forms of energy and can be stored easily. There already exists much infrastructure for transporting and distributing methane as well as infrastructure for converting methane into electricity and for powering vehicles. Methane also has the highest energy density per carbon atom of all fossil fuels, and therefore of all fossil fuels, methane releases the least carbon dioxide per unit energy when burned. Hence, systems for producing methane, e.g., through converting carbon dioxide and electricity into methane, would be highly useful and valuable in all energy generation and utilization industries.